The invention relates to a manufacturing method for a dispenser cathode for an electron gun used in ultralarge cathode ray tubes, projection tubes or hi-vision, etc., and, in particular, to a manufacturing method for a porous metal body of the cavity reservoir-type dispenser cathode.
In general, the structure of a cavity reservoir type dispenser cathode is as schematically illustrated in FIG. 1. A cup-type container 1 is mounted on the upper part of a sleeve 4 with a built-in heater 5, an electron emissive material 2 and a porous metal body 3 disposed in the container 1 in a stratiform shape.
The cavity reservoir type dispenser cathode as constructed above, as is well known, is capable of emitting electrons by a forming monoatomic layer from Ba diffused from below and from atoms contained in the porous metal body 3. The Ba diffuses from electron emissive material 2 due to the heat energy from the heater 5 through the pores of the porous metal body 3 and reaches the surface of the porous metal body. Since the ordinary operating temperature of such a dispenser cathode is 1050.degree. C. to 1200.degree. C., heat-resistant materials are required for making the dispenser cathode.
For example, the above-mentioned porous metal body is made of W, Mo, Ir or Os, whilst the container and the sleeve holding this porous metal body is W, Mo or Ta.
A good example of this kind of manufacturing method for cathodes is disclosed in U.S. Pat. No. 4,823,044. This patent describes that each component is manufactured through respective separate processes and then all components are assembled together. In this method, electron emissive material is disposed in the container and a porous metal body is sealingly mounted thereon by welding the porous metal body to the upper edge of the container. The welding is done with a high-powered laser welder, rather than an ordinary spot welder or gas welder.
Such a conventional manufacturing method has several disadvantages as described below, because it requires separate processes for producing the porous metal body and for welding the porous metal body to the container:
(A) The manufacturing process is complicated due to the separation of processes and the laser welder which is expensive. PA1 (B) The porous metal body may be damaged by the heat generated during welding. PA1 (C) Complete sealing between the porous metal body and the container cannot be expected and thus the electron emission ability may fall because the porous metal body is welded to the container at several spots.
Therefore, the object of the present invention is to provide a manufacturing method for a dispenser cathode for an electron gun whose manufacturing is simple and whose current density is improved.